Disc parking brakes for tractors are well known in the art. It has been proposed in the past to mount a disc brake construction on the output shaft of the transmission. In many tractors this presents serious design limitations as the differential housing is disposed immediately to the rear of the transmission, which differential housing also serves as an oil reservoir. Therefore, it is essential that the actuating mechanism for the parking brake be so designed that dirt and other foreign substances cannot be introduced into the differential housing at that place where it passes through the differential housing. One such prior art construction which achieves the foregoing objective is shown in Belgium Pat. No. 837,917. In accordance with the Belgium patent, a rotary shaft actuator is carried by a special member which is in turn secured to the periphery of a large opening in the sidewall of the differential housing. It should be appreciated, however, that the foregoing construction requires a special form of differential housing. As the tooling for providing such housings is very costly, it is desirable to provide a novel brake construction which can be utilized in existing differential housings.